Previously, there is known a fuel injection device that forms a gap in an axial direction between a movable core and a flange of a needle in such a manner that the movable core is accelerated in the gap and collides against the flange of the needle to implement valve opening of the needle. For example, the patent literature 1 discloses the fuel injection device that includes a gap forming member, which can form the gap in the axial direction between the movable core and the flange of the needle. In this fuel injection device, the movable core, which has an increased kinetic energy that is increased through the acceleration of the movable core in the gap, collides against the flange. Therefore, even though a fuel pressure in a fuel passage in an inside of a housing receiving the needle is high, the valve opening of the needle is possible. Thereby, the high pressure fuel can be injected.
In the fuel injection device of the patent literature 1, the gap forming member is shaped into a bottomed tubular form. An inner wall of a tubular portion of the gap forming member is slidable relative to an outer wall of the flange, and an outer wall of the tubular portion is slidable relative to an inner wall of the stationary core. In this way, reciprocation of the needle in an axial direction is guided. The needle is supported by the gap forming member and the stationary core only at one end part of the needle, which is opposite from a valve seat in the axial direction.
As discussed above, in the fuel injection device of the patent literature 1, the gap forming member has a double slide structure of that both of the inner wall and the outer wall of the tubular portion of the gap forming member are configured to slide along the other members. Therefore, a slide resistance, which is applied to the entire gap forming member, may possibly be increased, or wearing or uneven wearing of the slide surfaces may possibly occur upon a long time use. In this way, response of the needle may possibly be deteriorated, or reciprocation of the needle in the axial direction may possibly be unstabilized. Therefore, it may possibly cause variations in the injection amount of fuel injected from the fuel injection device. Furthermore, when the wear debris is generated, the wear debris may possibly be caught between corresponding members, which make relative movement therebetween, to possibly cause operational failure.
Furthermore, in the fuel injection device of the patent literature 1, the gap forming member has the double slide structure, so that the size management may become difficult, and the slide resistance may possibly vary from product-to-product. Thus, the injection amount of fuel may possibly vary among the fuel injection devices.